Multiple QNetworkRequests (post) with QNetworkNetworkAccessManager in a loop

[TimWoo]

As part of being a well-behaved netizen QNetworkAccessManager limits the number of simultaneous connections to a single server address. I am fairly sure this limit is 6 connections in the Qt5 source. Are all your connections to the same host?

Thanks for responding.

Only 1 host is concerned in this case. Is a new connection really created for every request in such a "batch" of 6? I don't think it explains why sometimes more than 6 requests (up to 11 observed so far) can be monitored on the network (and always the first n, no gaps in the sequence), do you have an explanation for this?

Please note that my code is written in Qt 4.7. Thought I'd mention it since you talk about Qt5.

I do not understand all the details of your code, but something caught my attention. The line

p->mReply = p->mManager->post(req, postReq);

p->mReply = p->mManager->post(req, postReq);

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overwrites the SyncPrivate's mReply member every time you send a request. Since all the requests made in the loop seem to go through the same Sync instance, I suppose that after the loop, mReply points to the last reply. Then, in Sync::replyFinished(), you always deal with that last reply, even if the slot is probably called for several of them. Here is a suggestion: instead of connecting to the QNetworkReply's finished() signal, consider connecting to QNetworkAccessManager::finished(QNetworkReply *) instead; that way, you get a pointer to the reply in the slot, right where you need it.

Good point I guess. That would explain why the application only reports replies for some of the requests. Do you think this would influence the behaviour of sending the requests?

[yeye_olive]

Good point I guess. That would explain why the application only reports replies for some of the requests. Do you think this would influence the behaviour of sending the requests?

I do not know the implementation details of QNetworkAccessManager, but it is entirely possible that the manager stops sending requests while too many QNetworkReply are around, waiting for the user to read their contents and then delete them.

[TimWoo]

@ChrisW67
Do you have any further insights?

@yeye_olive
I'm not familiar with the QNetworkAccessManager implementation myself, maybe someone else on the forum is? If so, I would very much welcome the input .

Further:
I cannot find any information about the maximum number of requests offered to QNetworkAccessManager simultaneously in the Qt 4.8 Documentation or anywhere else for that matter. I'm under the impression that it shouldn't be a problem for QNetworkAccessManager, but I could very well be wrong offcourse. It's all quite complex to me, as I'm still not quite familiar with asynchronous message handling.
I'm currently tempted to prototype a workaround to see if offering 6 requests to the QNAM at the same time solves the problem. I would then wait sending the next 6 requests once the previous 6 have been processed.

If anyone can shed some more light on the subject I would be very grateful.

Best Regards,

Tim